The invention relates to a display device for an actuator, and an actuator for a fitting having such a display device.
For activating actuating elements such as fittings, for example, as used in numerous processes in automotive engineering, in particular in power generation, water management, water conditioning, and the pharmaceutical, chemical, petroleum, and/or food industries, actuators are generally used which are designed as a part or section of the particular associated control loop or as part of the particular associated control device or process control system.
Actuators are currently used as a link between the control system and/or manufacturing execution system (MES) and the particular process in automated systems in practically all industrial sectors and fields in which material and/or mass variables are to be controlled or regulated. In this regard, the actuators used act primarily on fittings which are suitable for influencing or acting on the material or mass flow. These fittings include, among others, valves, plug valves, flap valves, or slide valves. A distinction may be made among different types of actuators, the differences relating essentially to the particular type of drive and operation, i.e., in particular whether such a drive is for control or regulation purposes, and whether the drive is operated pneumatically, hydraulically, electrically, or manually. Another option is differentiation according to the type of actuating motion, in particular whether the motion occurs in a linear, swiveling, or rotational manner.
The actuator is primarily designed as a rotary drive which acts with a torque on the particular fitting, in particular a threaded spindle or shaft of the fitting, for example via a threaded bushing or a reduction gear unit having a positive-fit connection with the shaft. The threaded spindle is connected at one end to a slide plate, for example, which may be displaced or moved by the applied torque in a guide between two end positions, from the “open” to the “shut” position, and vice versa.
To carry out the complete adjustment path, the so-called “fitting lift,” the actuator and/or the drive spindle must undergo from a few revolutions to several hundred to several thousand revolutions, depending on the fitting and the reduction gear unit. To also be able to obtain information concerning the particular adjustment position for an installed or inset fitting, the actuator includes a display device which is generally appropriately sealed, installed, and mounted in a housing for protection from soiling and/or moisture.
The particular display device may be designed as a mechanical, electromechanical, or electrical display, its essential task being to indicate the adjustment position and in particular the instantaneous lift of the particular fitting.
So that the particular adjustment position, in particular the adjustment lift, is retrievable or available at all times, in particular also for operation-related malfunctions of the fitting or failure of the actuator, for example during power interruptions, the use of mechanical display devices is recommended, in particular also with regard to safety aspects.
Such mechanical display devices generally include a gear unit which is coupled to the drive, in particular to the output drive shaft and/or the drive spindle, and a corresponding display element, for example a pointer, scale, dial, or the like, the gear unit causing a motion of the display element which is proportional to the number of revolutions of the spindle and/or the output drive shaft, by means of a predetermined, fixed gear ratio or reduction ratio. The proportionality factor is specified essentially by the design and length of the threaded spindle, and/or the gear ratio of the gear unit for torque multiplication, and/or the adjustment path of the fitting and thus of the possible number of revolutions of the output drive of the actuator between the two end positions of the fitting and the desired and/or available display range. Of course, the desired resolution and/or display accuracy also play a role here.
Since it is known that an actuator having a display device, when properly used, should be usable in the most universal manner possible for numerous different fittings having in particular different adjustment paths, and should meet the requirements thereof, a gear ratio which is adapted to same, and thus a corresponding gear unit or signal gear unit of the display device, must be selected or set up in each case as a function of the particular adjustment path or the gear reduction for torque generation. This occurs before the display device is installed or used, by an appropriate selection and matching of the individual toothed gears which form the gear unit.
Lastly, the particular display device is then installed in an appropriate housing, which is generally associated with the actuator, whereby appropriate sealing means may be provided between the display device and the housing and the various housing components in order to protect the display device and in particular the gear unit from contaminants and moisture, especially from functional impairment due to external influences.
Since the particular actuator is initially manufactured and marketed separately from the particular fitting, individual adjustment operations for the particular signal gear unit may be necessary before delivery or use for various uses or fields of application (adjustment paths, gear reductions).
To meet the above-mentioned requirements, either various types may be provided with a different fixed gear ratio, or a fixed gear reduction and therefore different signal gear units may be provided and prepared, which at least greatly increases the logistical complexity, and/or a variable-speed gear unit having different selectable gear ratios may be provided.
However, even for known display devices having a signal gear unit designed as a variable-speed gear unit, for changing boundary conditions and/or requirements, for example a replacement of the fitting and/or a change in the particular adjustment path of the fitting which requires adjustment of the gear ratio, it is disadvantageous that the display device must be removed from the housing and/or the drive in order to select a different gear ratio and/or to open the housing in order to adjust the particular signal gear unit. A measure which makes it necessary to open the housing or even to uninstall the display device, which removes—even if only temporarily—the protection of actuator components from environmental influences, or interferes with or interrupts the operational readiness of the display device as well as the entire drive and the fitting, is also referred to as “intrusive.” Conversely, measures or operations which require no such deinstallation and therefore essentially maintain and/or ensure the operational readiness of the display device and/or the drive and/or the fitting are also referred to as “nonintrusive.”
Thus, the issue is basically whether the desired or necessary manipulation or adaptation may be carried out without “intruding” (nonintrusively), with the advantage that damage from penetrating water, for example, is not possible during the actual operation or measure, or malfunction cannot result during or after reclosure on account of a wedged cable or improper seal, for example.
Thus, it is disadvantageous that opening the particular housing and/or removing the signal gear unit of the display device increases the risk of contamination or soiling, as well as the risk of malfunction (leaks, for example), in particular also as the result of faulty assembly.
Furthermore, the removal, replacement of the gear unit, and/or change of the gear ratio, as well as installing and sealing the housing, also entails a considerable level of effort.